Speaker
Description
44gSc presents a particular interest for application in nuclear medicine as a positron emission tomography (PET) radionuclide due to its favorable nuclear decay properties (t1/2 = 3.97 h, Emax = 1.47 MeV, branching ratio 94.3% β+). Its nuclear isomer 44mSc (t1/2 = 58.61 h) decays by isomeric transition (IT) into 44gSc, accompanied by ≈12% of conversion electron emission. So-called ‘after-effects’ caused by the emission of conversion electrons, which create a vacancy in the inner shells (K, L) followed by the Auger emission and other relaxation processes, may lead to complex disintegration when attached to the chelator, and consequently, to a partial release of the daughter.
Both 44mSc and 44gSc were produced via irradiation of natural Ca targets with 12.8 MeV protons. The further separation of Sc isomers from the target material was carried out using a direct-flow two-step radiochemical scheme, which includes DGA resin (branched, 50-100 μm) and HCl solutions, and cation-exchange resin Dowex 50Wx8 (200-400 mesh) and solution of ammonium α-hydroxyisobutyrate (NH4-α-HIB) [1]. The radiolabeling of DOTATOC (C=10-4 M, pH 5, 85°C, 60 min) with 44m/gSc was analyzed via instant thin layer chromatography (iTLC) and showed radiochemical yields of 98%. The system consisted of 44m/gSc attached to DOTATOC, Strata C-18E as a generator column and 0.1 M NH4-α-HIB as an eluent. The generator was eluted once a day with 0.1 M NH4-α-HIB. Quantification of the 44gSc yield and breakthrough of 44mSc was measured using γ-spectroscopy. The designed generator demonstrated 9.8±1.0% yield, which is close to the theoretical 12% yield (or ~80% per the portion of conversion). The breakthrough of the parent 44mSc was reduced from 3% during the first elution to 0.03% during the last elution (typically the generator was eluted 5-6 times). It is important to mention, that attempts to design a generator with 44m/gSc-DOTATATE on Strata X column resulted in low yields of less than 10% per the portion of conversion, which was also observed earlier by Huclier-Markai et al [2].
These results demonstrate the influence of after-effects on the stability of the initial complex, where 44gSc is one of the only examples with low Z. Moreover, this scheme would give the opportunity for generator sources of PET radionuclide - 44gSc to enable transport and kit labeling synthesis in the medical facility.
References
[1] Kurakina E.S. et al. Nucl. Med. Biol.104–105, 7 (2022).
[2] Huclier-Markai S et al. Nucl. Med. Biol. 41, e36 (2014)
